Adiponectin is a negative regulator of bone mineral and bone strength in growing mice

Effects of long term diabetogenic high fat diet on bone in ovariectomized female rats

A diabetogenic high fat diet (HFD) can be used to induce insulin resistance and obesity in animal models; however, its effects on bone are unknown. We investigated the effects of long term HFD on bone in ovariectomized (OVX) female rats. We used 12-week-old female rats divided randomly into four groups: sham operation (sham), sham operation with HFD (SHFD), OVX and OVX with HFD (OVX + HFD). Ovaries were removed in the OVX and OVX + HFD groups and the SHFD and OVX + HFD groups were fed a HFD for 28 weeks. Serum estrogen, testosterone, lipid, adiponectin, leptin, tartrate-resistant acid phosphatase (TRAP) and N-mid fragment of osteocalcin (N-MID-OT) levels were measured. Structure, apoptosis and specific transcription factors in bone were evaluated using pathologic, densitometric and immunohistochemical analysis. Body weight, serum leptin, TRAP and testosterone levels were increased, while serum N-MID-OT, estrogen and adiponectin levels were decreased in the SHFD, OVX and OVX + HFD groups. Expression of BCL2-associated X protein, caspase-3, matrix metalloproteinase-9 and calcitonin was increased, while bone mineral density (BMD) and content (BMC) in femurs and lumbar spine, and expression of B cell lymphoma 2, type 1 collagen and osteocalcin were decreased in the bones of the SHFD, OVX and OVX + HFD groups. All indices were greatest in the OVX + HFD group and HFD produced a detrimental effect on bone in both normal and OVX rats, which may be due to increased apoptosis in bone and increased leptin and decreased adiponectin levels in serum. The effects of HFD and OVX may be synergistic.

The Influence of Nesfatin-1 on Bone Metabolism Markers Concentration, Densitometric, Tomographic and Mechanical Parameters of Skeletal System of Rats in the Conditions of Established Osteopenia

Simple Summary

Nesfatin-1 is an adipokine with little known effect on the skeletal system. In this study, we examined the effect of 8-wk administration of nesfatin-1 on densitometric, tomographic, and mechanical parameters of bones, as well as the concentration of bone metabolism markers in rats with experimentally induced established osteopenia.

Abstract

Our study aimed to evaluate the impact of nesfatin-1 administration on bone metabolism and properties in established osteopenia in ovariectomized female rats. In total, 21 female Wistar rats were assigned to two groups: sham-operated (SHAM, n = 7) and ovariectomized (OVA, n = 14). After 12 weeks of osteopenia induction in the OVA females, the animals were given i.p. physiological saline (OVA, n = 7) or 2 µg/kg body weight of nesfatin-1(NES, n = 7) for the next 8 weeks. The SHAM animals received physiological saline at the same time. Final body weight, total bone mineral density and content of the skeleton were estimated. Then, isolated femora and tibias were subjected to densitometric, tomographic, and mechanical tests. Bone metabolism markers, i.e., osteocalcin, bone specific alkaline phosphatase (bALP), and crosslinked N-terminal telopeptide of type I collagen (NTx) were determined in serum using an ELISA kit. Ovariectomy led to negative changes in bone metabolism associated with increased resorption, thus diminishing the densitometric, tomographic, and mechanical parameters. In turn, the administration of nesfatin-1 led to an increase in the value of the majority of the tested parameters of bones. The lowest bALP concentration and the highest NTx concentration were found in the OVA females. The bALP concentration was significantly higher after nesfatin-1 administration in comparison to the OVA rats. In conclusion, the results indicate that nesfatin-1 treatment limits bone loss, preserves bone architecture, and increases bone strength in condition of established osteopenia.

An adiponectin receptor agonist promote osteogenesis via regulating bone-fat balance

OBJECTIVES

Adiponectin signalling has been considered to be a promising target to treat diabetes-related osteoporosis. However, contradictory results regarding bone formation were observed due to the various isoforms of adiponectin. Therefore, it would be necessary to investigate the effect of adiponectin receptor signals in regulating bone-fat balance.

MATERIALS AND METHODS

We primarily applied a newly found specific activator for adiponectin receptor, AdipoRon, to treat bone metabolism-related cells to investigate the role of Adiponectin receptor signals on bone-fat balance. We then established femur defect mouse model and treated them with AdipoRon to see whether adiponectin receptor activation could promote bone regeneration.

RESULTS

We found that AdipoRon could slightly inhibit the proliferation of pre-osteoblast and pre-osteoclast, but AdipoRon showed no effect on the viability of mesenchymal stromal cells. AdipoRon could remarkably promote cell migration of mesenchymal stromal cells. Additionally, AdipoRon promoted osteogenesis in both pre-osteoblasts and mesenchymal cells. Besides, AdipoRon significantly inhibited osteoclastogenesis via its direct impact on pre-osteoclast and its indirect inhibition of RANKL in osteoblast. Moreover, mesenchymal stromal stems cells showed obviously decreased adipogenesis when treated with AdipoRon. Consistently, AdipoRon-treated mice showed faster bone regeneration and repressed adipogenesis.

CONCLUSIONS

Our study demonstrated a pro-osteogenic, anti-adipogenic and anti-osteoclastogenic effect of adiponectin receptor activation in young mice, which suggested adiponectin receptor signalling was involved in bone regeneration and bone-fat balance regulation.

APPL1 negatively regulates bone mass, possibly by controlling the fate of bone marrow mesenchymal progenitor cells

Adiponectin is an adipokine that can exert a regulatory function on bone metabolism. However, there are many contradictions between clinical and pre-clinical studies on adiponectin. APPL1 is an adaptor protein that can interact with adiponectin receptors. In the current study, we found that knockout of the Appl1 gene in male mice was associated with higher bone volume and numbers of trabeculae than in females or controls. The trabecular thickness, cortical thickness, ratio of bone volume/trabecular volume, cross-sectional bone area, and mean polar moment of inertia increased in Appl1 KO mice compared with wild-type mice. The number of osteoblasts increased but the number of adipocytes decreased in Appl1 KO mice. Knockdown of Appl1 impaired adipogenesis in bone marrow-derived mesenchymal stem cells. Mineralization was increased by knockdown of Appl1 during osteoblast differentiation. Data from differentiation-related genes showed results consistent with the in vivo effects. In summary, this study provides further clarification of the effect of the adiponectin signaling pathway on bone metabolism.

KS23, a novel peptide derived from adiponectin, inhibits retinal inflammation and downregulates the proportions of Th1 and Th17 cells during experimental autoimmune uveitis

BACKGROUND

Uveitis is a potentially sight-threatening form of ocular inflammation that affects the uvea in the wall of the eye. Currently available treatments for uveitis have exhibited profound adverse side effects. However, KS23 is a novel 23-amino-acid anti-inflammatory peptide derived from adiponectin that may have the capability to function as a safe alternative to these existing treatment options. We, therefore, evaluated the preventive effect of KS23 in experimental autoimmune uveitis (EAU).

METHODS

EAU was induced in mice via immunization with the peptide interphotoreceptor retinoid binding protein 161-180 (IRBP161-180). KS23 was then administered every 2 days via intraperitoneal injection to induce protection against EAU. Clinical and histopathological scores were employed to evaluate the disease progression. Inflammatory cytokines were also quantified using ELISA, and the expression levels of specific chemokines and chemokine receptors were assessed via qRT-PCR. In addition, the proportions of Th1 and Th17 cells were detected via flow cytometry, and the expression levels of specific proteins were quantified from the retina of mice using western blot analysis, to elucidate the specific mechanism of action employed by KS23 to suppress the inflammation associated with EAU.

RESULTS

KS23 was found to significantly improve EAU-associated histopathological scores, while decreasing the expression of pro-inflammatory cytokines (IFN-γ, TNF-α, IL-6, and IL-17A), chemokines (LARC, RANTES, MIG, IP-10), and chemokine receptors (CCR6 and CXCR3). The proportions of Th1 and Th17 cells were also suppressed following intraperitoneal injection with KS23. The anti-inflammatory mechanism employed by KS23 was determined to be associated with the activation of AMPK and subsequent inhibition of NF-κB.

CONCLUSIONS

KS23 decreased the proportions of Th1 and Th17 cells to effectively ameliorate the progression of EAU. It may, therefore, serve as a promising potential therapeutic agent for uveitis.

Effect of adiponectin secreted from adipose-derived stem cells on bone-fat balance and bone defect healing

The efficacy of adiponectin (APN) in regulating bone metabolism remains controversial. This study aimed to investigate the role of APN secreted from adipose-derived stem cells on adipogenesis and osteogenesis. Human APN gene was transfected via recombinant adenovirus into adipose derived stem cells (ASCs) in vitro and were cocultured with bone marrow mesenchymal stem cells (BMSCs) in using a transwell chamber. Adipogenesis was inhibited in APN-transfected ASCs; in BMSCs, adipogenesis was inhibited, but osteogenesis was promoted in coculture with APN-transfected ASCs. Next, the same adenovirus construct was transfected into the abdominal adipose tissue of a Sprague Dawley rat in vivo, and then a tibia defect was established in the same rat. We confirmed there was higher gene and protein expression of APN in ASCs and the abdominal adipose tissue of these rat models. Development of adipocytes in abdominal adipose tissue was suppressed, and less new bone was formed in the bone defect area. In conclusion, APN secreted from ASCs could directly inhibit adipogenesis in ASCs and BMSCs and promote osteogenesis in the latter. However, APN overexpression in adipose tissue was inversely associated with bone formation in tibia defects potentially due to decreased levels of circulating bone-activating hormones.

Adipose Tissue, Obesity and Adiponectin: Role in Endocrine Cancer Risk

Adipose tissue has been recognized as a complex organ with endocrine and metabolic roles. The excess of fat mass, as occurs during overweight and obesity states, alters the regulation of adipose tissue, contributing to the development of obesity-related disorders. In this regard, many epidemiological studies shown an association between obesity and numerous types of malignancies, comprising those linked to the endocrine system (e.g., breast, endometrial, ovarian, thyroid and prostate cancers). Multiple factors may contribute to this phenomenon, such as hyperinsulinemia, dyslipidemia, oxidative stress, inflammation, abnormal adipokines secretion and metabolism. Among adipokines, growing interest has been placed in recent years on adiponectin (APN) and on its role in carcinogenesis. APN is secreted by adipose tissue and exerts both anti-inflammatory and anti-proliferative actions. It has been demonstrated that APN is drastically decreased in obese individuals and that it can play a crucial role in tumor growth. Although literature data on the impact of APN on carcinogenesis are sometimes conflicting, the most accredited hypothesis is that it has a protective action, preventing cancer development and progression. The aim of the present review is to summarize the currently available evidence on the involvement of APN and its signaling in the etiology of cancer, focusing on endocrine malignancies.

Mechanisms of Adiponectin Action: Implication of Adiponectin Receptor Agonism in Diabetic Kidney Disease

Adiponectin, an adipokine secreted by adipocytes, exerts favorable effects in the milieu of diabetes and metabolic syndrome through its anti-inflammatory, antifibrotic, and antioxidant effects. It mediates fatty acid metabolism by inducing AMP-activated protein kinase (AMPK) phosphorylation and increasing peroxisome proliferative-activated receptor (PPAR)-α expression through adiponectin receptor (AdipoR)1 and AdipoR2, respectively, which in turn activate PPAR gamma coactivator 1 alpha (PGC-1α), increase the phosphorylation of acyl CoA oxidase, and upregulate the uncoupling proteins involved in energy consumption. Moreover, adiponectin potently stimulates ceramidase activity associated with its two receptors and enhances ceramide catabolism and the formation of its anti-apoptotic metabolite, sphingosine 1 phosphate (S1P), independently of AMPK. Low circulating adiponectin levels in obese patients with a risk of insulin resistance, type 2 diabetes, and cardiovascular diseases, and increased adiponectin expression in the state of albuminuria suggest a protective and compensatory role for adiponectin in mitigating further renal injury during the development of overt diabetic kidney disease (DKD). We propose AdipoRon, an orally active synthetic adiponectin receptor agonist as a promising drug for restoration of DKD without inducing systemic adverse effects. Its renoprotective role against lipotoxicity and oxidative stress by enhancing the AMPK/PPARα pathway and ceramidase activity through AdipoRs is revealed here.

Adiponectin Deficiency Triggers Bone Loss by Up-Regulation of Osteoclastogenesis and Down-Regulation of Osteoblastogenesis

Osteoporosis and bone disorders related to the metabolic syndrome are often associated with adipokines secreted by adipocytes in bone. Adiponectin, a type of adipokine, is a regulator of immune responses and metabolic processes, but its role in bone biology remains uncertain. We investigated the role of adiponectin in bone metabolism using adiponectin-deficient mice in vivo and in vitro. Adiponectin-deficient mice exhibited reduced bone mass and increased adiposity. Adiponectin-deficient calvarial cells were prone to differentiate into adipocytes rather than osteoblasts. Although bone marrow macrophages (BMMs) from adiponectin-deficient mice had low osteoclastogenic potential as osteoclast precursors with increasing interferon regulatory factor 5 expression, under co-culture conditions of calvarial cells and BMMs, the enhanced receptor activator of nuclear factor κB ligand/osteoprotegerin (RANKL/OPG) ratio of adiponectin-deficient mesenchymal progenitor cells facilitated osteoclast differentiation. In addition, increased RANKL/OPG ratio was observed in the bone marrow extracellular fluid of adiponectin-deficient mice compared to that of wild-type mice. Notably, recombinant adiponectin treatment enhanced RANKL-induced osteoclast differentiation from BMMs but up-regulated OPG production in recombinant adiponectin-exposed calvarial cells, which inhibited osteoclast differentiation. Taken together, these results suggest that adiponectin plays an inhibitory role in bone metabolism through cross talk between precursor cells of both osteoclasts and osteoblasts by regulating RANKL/OPG ratio in the bone marrow microenvironment.

Effects of Anorexia Nervosa on Bone Metabolism

Anorexia nervosa is a psychiatric disease characterized by a low-weight state due to self-induced starvation. This disorder, which predominantly affects women, is associated with hormonal adaptations that minimize energy expenditure in the setting of low nutrient intake. These adaptations include GH resistance, functional hypothalamic amenorrhea, and nonthyroidal illness syndrome. Although these adaptations may be beneficial to short-term survival, they contribute to the significant and often persistent morbidity associated with this disorder, including bone loss, which affects >85% of women. We review the hormonal adaptions to undernutrition, review hormonal treatments that have been studied for both the underlying disorder as well as for the associated decreased bone mass, and discuss the important challenges that remain, including the lack of long-term treatments for bone loss in this chronic disorder and the fact that despite recovery, many individuals who experience bone loss as adolescents have chronic deficits and an increased risk of fracture in adulthood.

Adiponectin signaling and its role in bone metabolism

Adiponectin, the most prevalent adipo-cytokine in plasma plays critical metabolic and anti-inflammatory roles is fast emerging as an important molecular target for the treatment of metabolic disorders. Adiponectin action is critical in multiple organs including cardio-vascular system, muscle, liver, adipose tissue, brain and bone. Adiponectin signaling in bone has been a topic of active investigation lately. Human association studies and multiple mice models of gene deletion/modification failed to define a clear cause and effect of adiponectin signaling in bone. The most plausible reason could be the multimeric forms of adiponectin that display differential binding to receptors (adipoR1 and adipoR2) with cell-specific receptor variants in bone. Discovery of small molecule agonist of adipoR1 suggested a salutary role of this receptor in bone metabolism. The downstream signaling of adipoR1 in osteoblasts involves stimulation of oxidative phosphorylation leading to increased differentiation via the likely suppression of wnt inhibitor, sclerostin. On the other hand, the inflammation modulatory effect of adiponectin signaling suppresses the RANKL (receptor activator of nuclear factor κ-B ligand) - to - OPG (osteprotegerin) ratio in osteoblasts leading to the suppression of osteoclastogenic response. This review will discuss the adiponectin signaling and its role in skeletal homeostasis and critically assess whether adipoR1 could be a therapeutic target for the treatment of metabolic bone diseases.

The temporal expression of adipokines during spinal fusion

BACKGROUND CONTEXT

Adipokines are secreted by white adipose tissue and have been associated with fracture healing. Our goal was to report the temporal expression of adipokines during spinal fusion in an established rabbit model.

PURPOSE

Our goal was to report the temporal expression of adipokines during spinal fusion in an established rabbit model.

STUDY DESIGN

The study design included a laboratory animal model.

METHODS

New Zealand white rabbits were assigned to either sham surgery (n=2), unilateral posterior spinal fusion (n=14), or bilateral posterior spinal fusion (n=14). Rabbits were euthanized 1-6 and 10 weeks out from surgery. Fusion was evaluated by radiographs, manual palpation, and histology. Reverse transcription-polymerase chain reaction on the bone fusion mass catalogued the gene expression of leptin, adiponectin, resistin, and vascular endothelial growth factor (VEGF) at each time point. Results were normalized to the internal control gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (2^ΔCt), and control bone sites (2^ΔΔCt). Quantitative data were analyzed by two-factor analysis of variance (p<.05).

RESULTS

Manual palpation scores, radiograph scores, and histologic findings showed progression of boney fusion over time (p<.0003). The frequency of fusion by palpation after 4 weeks was 68.75%. Leptin expression in decortication and bone graft sites peaked at 5 weeks after the fusion procedure (p=.0143), adiponectin expression was greatest 1 week after surgery (p<.001), VEGF expression peaked at 4 weeks just after initial increases in leptin expression (p<.001), and resistin decreased precipitously 1 week after the fusion procedure (p<.001).

CONCLUSIONS

Leptin expression is likely associated with the maturation phase of bone fusion. Adiponectin and resistin may play a role early on during the fusion process. Our results suggest that leptin expression may be upstream of VEGF expression during spinal fusion, and both appear to play an important role in bone spinal fusion.

Serum adiponectin predicts fracture risk in individuals with type 2 diabetes: the Fukuoka Diabetes Registry

AIMS/HYPOTHESIS

Serum adiponectin has been reported to impact upon fracture risk in the general population. Although type 2 diabetes is associated with increased fracture risk, it is unclear whether serum adiponectin predicts fractures in individuals with type 2 diabetes. The aim of the study was to prospectively investigate the relationship between serum adiponectin and fracture risk in individuals with type 2 diabetes.

METHODS

In this study, data was obtained from The Fukuoka Diabetes Registry, a multicentre prospective study designed to investigate the influence of modern treatments on the prognoses of patients with diabetes mellitus. We followed 4869 participants with type 2 diabetes (mean age, 65 years), including 1951 postmenopausal women (defined as self-reported amenorrhea for >1 year) and 2754 men, for a median of 5.3 years. The primary outcomes were fractures at any site and major osteoporotic fractures (MOFs).

RESULTS

During the follow-up period, fractures at any site occurred in 682 participants, while MOFs occurred in 277 participants. Age-adjusted HRs (95% CIs) of any fracture and MOFs for 1 SD increment in log _e -transformed serum adiponectin were 1.27 (1.15, 1.40) and 1.35 (1.17, 1.55) in postmenopausal women and 1.22 (1.08, 1.38) and 1.40 (1.15, 1.71) in men, respectively. HRs (95% CIs) of MOFs for hyperadiponectinaemia (≥ 20 μg/ml) were 1.72 (1.19, 2.50) in postmenopausal women and 2.19 (1.23, 3.90) in men. The per cent attributable risk of hyperadiponectinaemia for MOFs was as high as being age ≥70 years or female sex.

CONCLUSIONS/INTERPRETATION

Higher serum adiponectin levels were significantly associated with an increased risk of fractures at any site and with an increased risk of MOFs in individuals with type 2 diabetes, including postmenopausal women.

The Activity of Adiponectin in Bone

The adipokine adiponectin affects multiple target tissues and plays important roles in glucose metabolism and whole-body energy homeostasis. Circulating adiponectin levels in obese people are lower than in non-obese, and increased serum adiponectin is associated with weight loss. Numerous clinical studies have established that fat mass is positively related to bone mass, a relationship that is maintained by communication between the two tissues through hormones and cytokines. Since adiponectin levels inversely correspond to fat mass, its bone effects and its potential contribution to the relationship between fat and bone have been investigated. In clinical observational studies, adiponectin was found to be negatively associated with bone mineral density, suggesting it might be a negative regulator of bone metabolism. In order to identify the mechanisms that underlie the activity of adiponectin in bone, a large number of laboratory studies in vitro and in animal models of mice over-expressing or deficient of adiponectin have been carried out. Results of these studies are not entirely congruent, partly due to variation among experimental systems and partly due to the complex nature of adiponectin signaling, which involves a combination of multiple direct and indirect mechanisms.

Adiponectin alters renal calcium and phosphate excretion through regulation of klotho expression

The kidney controls systemic calcium and phosphate levels and disturbances of its control mechanisms can lead to a variety of diseases. The insulin-sensitizing adipokine adiponectin is renoprotective and accelerates functional recovery following renal injury. However, unlike other adipokines, adiponectin is reduced in obesity. High adiponectin levels are also correlated with bone loss, suggestive of an additional action in mineral metabolism. Using knockout, wild-type, and adiponectin-overexpressing transgenic mice, we sought to identify the mechanistic basis for adiponectin's ability to regulate calcium and phosphate balance at the level of the kidney. Adiponectin knockout mice exhibited lower serum calcium, lower urinary calcium excretion, and markedly lower serum fibroblast growth factor 23 (FGF23) levels, although circulating klotho concentrations were significantly higher than in wild-type littermates. The transgenic mice exhibited lower bone mass and strength, particularly compared to adiponectin knockout mice. The transgenic mice were hyper-responsive to a 2% phosphate-enriched diet, exhibiting 2-fold higher serum FGF23 and concomitantly higher fractional phosphate excretion. These mice also excreted more calcium with calcium-enriched diet and had less renal klotho protein expression. In contrast, the knockout mice exhibited a smaller increase in FGF23 and maintained elevated klotho levels on both mineral challenges. Kidney-specific adiponectin expression in doxycycline-inducible adiponectin mice and adiponectin addition in vitro confirmed adiponectin's ability to reduce tubular epithelial cell klotho secretion. Thus, adiponectin alters calcium and phosphate balance and renal mineral excretion, in part, through klotho. This work highlights the profound effects of adipose tissue on renal function and has identified a new mechanism by which adiponectin may regulate bone mass.

Obesity is a concern for bone health with aging

Accumulating evidence supports a complex relationship between adiposity and osteoporosis in overweight/obese individuals, with local interactions and endocrine regulation by adipose tissue on bone metabolism and fracture risk in elderly populations. This review was conducted to summarize existing evidence to test the hypothesis that obesity is a risk factor for bone health in aging individuals. Mechanisms by which obesity adversely affects bone health are believed to be multiple, such as an alteration of bone-regulating hormones, inflammation, oxidative stress, the endocannabinoid system, that affect bone cell metabolism are discussed. In addition, evidence on the effect of fat mass and distribution on bone mass and quality is reviewed together with findings relating energy and fat intake with bone health. In summary, studies indicate that the positive effects of body weight on bone mineral density cannot counteract the detrimental effects of obesity on bone quality. However, the exact mechanism underlying bone deterioration in the obese is not clear yet and further research is required to elucidate the effect of adipose depots on bone and fracture risk in the obese population.

Reduced Bone Density and Cortical Bone Indices in Female Adiponectin-Knockout Mice

A positive association between fat and bone mass is maintained through a network of signaling molecules. Clinical studies found that the circulating levels of adiponectin, a peptide secreted from adipocytes, are inversely related to visceral fat mass and bone mineral density, and it has been suggested that adiponectin contributes to the coupling between fat and bone. Our study tested the hypothesis that adiponectin affects bone tissue by comparing the bone phenotype of wild-type and adiponectin-knockout (APN-KO) female mice between the ages of 8-37 weeks. Using a longitudinal study design, we determined body composition and bone density using dual energy x-ray absorptiometry. In parallel, groups of animals were killed at different ages and bone properties were analyzed by microcomputed tomography, dynamic histomorphometry, 3-point bending test, nanoindentation, and computational modelling. APN-KO mice had reduced body fat and decreased whole-skeleton bone mineral density. Microcomputed tomography analysis identified reduced cortical area fraction and average cortical thickness in APN-KO mice in all the age groups and reduced trabecular bone volume fraction only in young APN-KO mice. There were no major differences in bone strength and material properties between the 2 groups. Taken together, our results demonstrate a positive effect of adiponectin on bone geometry and density in our mouse model. Assuming adiponectin has similar effects in humans, the low circulating levels of adiponectin associated with increased fat mass are unlikely to contribute to the parallel increase in bone mass. Therefore, adiponectin does not appear to play a role in the coupling between fat and bone tissue.

Resveratrol increases AdipoR1 and AdipoR2 expression in type 2 diabetic nephropathy

BACKGROUND

Adiponectin has multiple functions including insulin sensitization, anti-inflammation and antiatherogenesis in various organs. Adiponectin activates 5'-adenosine monophosphate-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor (PPAR)α via the adiponectin receptor (AdipoR) 1 and 2, which are critical for regulating lipids and glucose homeostasis and for controlling oxidative stress. We investigated whether resveratrol can inhibit renal damage in type 2 diabetic db/db mice and the underlying mechanisms of its effects.

METHODS

Four groups of male C57 BLKS/J db/m and db/db mice and human glomerular endothelial cells (HGECs) were used. Resveratrol was administered to diabetic and nondiabetic mice by oral gavage for 12 weeks starting at 8 weeks of age.

RESULTS

In db/db mice, resveratrol increased serum adiponectin levels and decreased albuminuria, glomerular matrix expansion, inflammation and apoptosis in the glomerulus. Resveratrol increased the phosphorylation of AMPK and silent information regulator T1 (SIRT1), and decreased phosphorylation of downstream effectors class O forkhead box (FoxO)1 and FoxO3a via increasing AdipoR1 and AdipoR2 in the renal cortex. Furthermore, resveratrol increased expression of PPARγ coactivator (PGC)-1α, estrogen-related receptor-1α, and phosphorylated acetyl-CoA carboxylase and decreased sterol regulatory element-binding protein 1. This effect lowered the content of nonesterified fatty acid and triacylglycerol in the kidneys, decreasing apoptosis, oxidative stress and activating endothelial nitric oxide synthase. Resveratrol prevented cultured HGECs from undergoing high-glucose-induced oxidative stress and apoptosis by activating the AMPK-SIRT1-PGC-1α axis and PPARα through increases in AdipoR1 and AdipoR2 expression.

CONCLUSIONS

These results suggest that resveratrol prevents diabetic nephropathy by ameliorating lipotoxicity, oxidative stress, apoptosis and endothelial dysfunction via increasing AdipoR1 and AdipoR2 expression.

Targeting adipose tissue in the treatment of obesity-associated diabetes

Adipose tissue regulates numerous physiological processes, and its dysfunction in obese humans is associated with disrupted metabolic homeostasis, insulin resistance and type 2 diabetes mellitus (T2DM). Although several US-approved treatments for obesity and T2DM exist, these are limited by adverse effects and a lack of effective long-term glucose control. In this Review, we provide an overview of the role of adipose tissue in metabolic homeostasis and assess emerging novel therapeutic strategies targeting adipose tissue, including adipokine-based strategies, promotion of white adipose tissue beiging as well as reduction of inflammation and fibrosis.

Evolving role of adiponectin in cancer-controversies and update

Adiponectin (APN), an adipokine produced by adipocytes, has been shown to have a critical role in the pathogenesis of obesity-associated malignancies. Through its receptor interactions, APN may exert its anti-carcinogenic effects including regulating cell survival, apoptosis and metastasis via a plethora of signalling pathways. Despite the strong evidence supporting this notion, some work may indicate otherwise. Our review addresses all controversies critically. On the whole, hypoadiponectinaemia is associated with increased risk of several malignancies and poor prognosis. In addition, various genetic polymorphisms may predispose individuals to increased risk of obesity-associated malignancies. We also provide an updated summary on therapeutic interventions to increase APN levels that are of key interest in this field. To date efforts to manipulate APN levels have been promising, but much work remains to be done.

Relationships between serum Omentin-1 levels and bone mineral density in older men with osteoporosis

OBJECTIVE

To investigate the correlation between serum Omentin-1 levels and the presence of osteoporosis in older men.

METHODS

Serum Omentin-1, bone turnover biochemical markers, and bone mineral density (BMD) were determined in 45 older men with osteoporosis or 45 older men without osteoporosis (65-70 years old).

RESULTS

Omentin-1 levels were increased in older men with osteoporosis, and the differences remained significant after controlling for fat mass. Omentin-1 was negatively correlated with BMD. In a multiple linear stepwise regression analysis, Omentin-1, lean mass, but not fat mass, were independent predictors of BMD for the combined group. Significant negative correlations between Omentin-1 and bone-specific alkaline phosphatase (BAP) and bone cross-linked N-telopeptides of type Ⅰ collagen (NTX) were found. Omentin-1 was also independently associated with BMD and bone turnover markers in older men with osteoporosis and control groups that were considered separately.

CONCLUSIONS

Omentin-1 is an independent predictor of BMD in older men with osteoporosis, and it is negatively correlated with bone turnover biochemical markers. It is suggested that Omentin-1 may exert a negative effect on bone mass through the regulation of the osteoblast differentiation in the older men with osteoporosis.

Adenosine monophosphate-activated protein kinase in diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, and its pathogenesis is complex and has not yet been fully elucidated. Abnormal glucose and lipid metabolism is key to understanding the pathogenesis of DN, which can develop in both type 1 and type 2 diabetes. A hallmark of this disease is the accumulation of glucose and lipids in renal cells, resulting in oxidative and endoplasmic reticulum stress, intracellular hypoxia, and inflammation, eventually leading to glomerulosclerosis and interstitial fibrosis. There is a growing body of evidence demonstrating that dysregulation of 5′ adenosine monophosphate–activated protein kinase (AMPK), an enzyme that plays a principal role in cell growth and cellular energy homeostasis, in relevant tissues is a key component of the development of metabolic syndrome and type 2 diabetes mellitus; thus, targeting this enzyme may ameliorate some pathologic features of this disease. AMPK regulates the coordination of anabolic processes, with its activation proven to improve glucose and lipid homeostasis in insulin-resistant animal models, as well as demonstrating mitochondrial biogenesis and antitumor activity. In this review, we discuss new findings regarding the role of AMPK in the pathogenesis of DN and offer suggestions for feasible clinical use and future studies of the role of AMPK activators in this disorder.

Negative Skeletal Effects of Locally Produced Adiponectin

Epidemiological studies show that high circulating levels of adiponectin are associated with low bone mineral density. The effect of adiponectin on skeletal homeostasis, on osteoblasts in particular, remains controversial. We investigated this issue using mice with adipocyte-specific over-expression of adiponectin (AdTg). MicroCT and histomorphometric analysis revealed decreases (15%) in fractional bone volume in AdTg mice at the proximal tibia with no changes at the distal femur. Cortical bone thickness at mid-shafts of the tibia and at the tibiofibular junction was reduced (3–4%) in AdTg mice. Dynamic histomorphometry at the proximal tibia in AdTg mice revealed inhibition of bone formation. AdTg mice had increased numbers of adipocytes in close proximity to trabecular bone in the tibia, associated with increased adiponectin levels in tibial marrow. Treatment of BMSCs with adiponectin after initiation of osteoblastic differentiation resulted in reduced mineralized colony formation and reduced expression of mRNA of osteoblastic genes, osterix (70%), Runx2 (52%), alkaline phosphatase (72%), Col1 (74%), and osteocalcin (81%). Adiponectin treatment of differentiating osteoblasts increased expression of the osteoblast genes PPARγ (32%) and C/ebpα (55%) and increased adipocyte colony formation. These data suggest a model in which locally produced adiponectin plays a negative role in regulating skeletal homeostasis through inhibition of bone formation and by promoting an adipogenic phenotype.

Pros and cons of fatty acids in bone biology

Despite the growing interest in deciphering the causes and consequences of obesity-related disorders, the mechanisms linking fat intake to bone behaviour remain unclear. Since bone fractures are widely associated with increased morbidity and mortality, most notably in elderly and obese people, bone health has become a major social and economic issue. Consistently, public health system guidelines have encouraged low-fat diets in order to reduce associated complications. However, from a bone point of view, mechanisms linking fat intake to bone alteration remain quite controversial. Thus, after more than a decade of dedicated studies, this timely review offers a comprehensive overview of the relationships between bone and fatty acids. Using clinical evidences as a starting-point to more complex molecular elucidation, this work highlights the complexity of the system and reveals that bone alteration that cannot be solved simply by taking ω-3 pills. Fatty acid effects on bone metabolism can be both direct and indirect and require integrated investigations. Furthermore, even at the level of a single cell, one fatty acid is able to trigger several different independent pathways (receptors, metabolites…) which may all have a say in the final cellular metabolic response.

Lipid metabolism disorders and bone dysfunction--interrelated and mutually regulated (review)

The association between lipid and bone metabolism has become an increasing focus of interest in recent years, and accumulating evidence has shown that atherosclerosis (AS) and osteoporosis (OP), a disorder of bone metabolism, frequently co-exist. Fat and bone are known to share a common progenitor cell: Multipotent mesenchymal stem cells (MSC) in the bone marrow (BM), which are able to differentiate into various cell phenotypes, including osteoblasts, adipocytes and chondrocytes. Laboratory-based and clinical trials have shown that increasing adipocytes are accompanied by a decrease in bone mineral density (BMD) and bone mass. Statins, lipid-lowering drugs used to treat hyperlipidemia, also provide benefit in the treatment of OP. There is thus evidence that the metabolism of lipids is correlated with that of bone, and that the two are mutually regulated. The present review primarily focuses on the potential association between lipid metabolism disturbance and OP, based on biological metabolism, pathophysiological processes, results from clinical and experimental animal studies, processes involved in the differentiation of adipocytes and osteoblasts, as well as pharmacological treatments of these diseases.

Adiponectin exerts its negative effect on bone metabolism via OPG/RANKL pathway: an in vivo study

To explore the effects of adiponectin on the bone metabolism in vivo. Bone mineral density (BMD), bone microstructure, serum adiponectin levels, and biochemical markers of the bone turnover were measured in 12-week-old male Adipo-/- and WT mice. In addition, the osteoclast formation, osteoprotegerin (OPG), and the receptor activator of nuclear factor-κB ligand (RANKL) expression were examined. The serum adiponectin levels were normal in the WT mice while undetectable in the Adipo-/- mice. Compared with the WT mice, the Adipo-/- mice had higher BMD, more trabecular bone, greater bone volume fraction, and trabecular thickness in the left femur. On the contrary, fewer osteoclasts were observed in the Adipo-/- mice when compared with the WT mice. Meanwhile, the Adipo-/- mice had a significantly decreased serum carboxyl-terminal telopeptide of type 1 collagen (CTX)/osteocalcin (OC) ratio. Interestingly, both the adiponectin and RANKL would cause a significant increase of CTX/OC ratio in the co-culture of the CD14+ peripheral blood mononuclear cells and the osteoblasts from Adipo-/- mice. Further, immunohistochemistry assays in tibias and both the RT-PCR and immunoblot analyses in the cultured osteoblasts showed the Adipo-/- mice expressed lower levels of RANKL but higher levels of OPG. Adiponectin had a negative effect on the bone metabolism, and this negative effect might be mediated, at least in part, by the OPG/RANKL pathway.

Anorexia nervosa and bone metabolism

Anorexia nervosa (AN) is a psychiatric disorder characterized by self-induced starvation with a lifetime prevalence of 2.2% in women. The most common medical co-morbidity in women with AN is bone loss, with over 85% of women having bone mineral density values more than one standard deviation below an age comparable mean. The low bone mass in AN is due to multiple hormonal adaptations to under nutrition, including hypothalamic amenorrhea and growth hormone resistance. Importantly, this low bone mass is also associated with a seven-fold increased risk of fracture. Therefore, strategies to effectively prevent bone loss and increase bone mass are critical. We will review hormonal adaptations that contribute to bone loss in this population as well as promising new therapies that may increase bone mass and reduce fracture risk in AN.

Adiponectin receptor 1 regulates bone formation and osteoblast differentiation by GSK-3β/β-catenin signaling in mice

Adiponectin and its receptors are expressed in bone marrow-derived osteoblasts. Previous studies in vivo and in vitro have produced controversial results. The purpose of this study was to use porcine adiponectin receptor 1 transgenic mice (pAdipoR1) as a model to evaluate the role of AdipoR1 on bone physiology at different ages. pAdipoR1 transgenic mice had higher bone mineral density than wild-type mice in both genders at 56 weeks of age. The bone volume and trabecular number, measured by micro-computed tomography (μCT) was significantly greater in transgenic than in wild-type female mice at both 8 and 56 weeks of age. ELISA analysis revealed that both serum osteocalcin and osteoprotegerin (OPG) were significantly increased in 8-week old pAdipoR1 transgenic mice of both genders. Furthermore, serum OPG was elevated at 32 and 56 weeks of age in female and male pAdipoR1 transgenic mice. Serum TRAP5b concentration was reduced in 8 and 56 weeks old male pAdipoR1 mice compared with wild-type male mice. Knock-down of AdipoR1 significantly decreased gene expression of osteocalcin, OPG, alkaline phosphatase and msh homeobox 2 and the mineralization in MC3T3-E1 cells and mesenchymal stem cells. In addition, pathscan analysis and real-time PCR analysis suggest AdipoR1 regulates osteoblast differentiation through GSK-3 β and β-Catenin signaling. Consequently, the lack of AdipoR1 impaired osteoblast differentiation and bone formation. We conclude that AdipoR1 is a critical factor for the osteoblast differentiation and bone homeostasis.

Relationships between serum adipocyte hormones (adiponectin, leptin, resistin), bone mineral density and bone metabolic markers in osteoporosis patients

The purpose of this study was to investigate the relationship between fasting serum leptin, adiponectin and resistin levels and bone mineral density (BMD) in osteoporosis patients and a non-osteoporosis control group. We studied 81 non-diabetic osteoporosis patients (92 % female, 8 % male; mean age 54.5 ± 15.5 years and body mass index [BMI] 28.2 ± 4.6) and 120 non-diabetic individuals with normal BMD as controls (86 % female, 14 % male; mean age 39.7 ± 10.4 years and BMI 28.8 ± 4.4). BMD was studied by dual-energy X-ray absorptiometry from the lumbar spine (L1-L4) and femoral neck and fasting blood samples were taken for biochemical measurement of fasting blood glucose, leptin, adiponectin and resistin. Fasting levels of plasma adiponectin had a significant negative correlation with BMD of the femoral neck and lumbar spine in the osteoporosis group (r = -0.478, P = 0.003, r = -0.513, P = 0.023) but not in the non-osteoporosis group (r = -0.158, P = 0.057, r = -0.23, P = 0.465). Fasting plasma levels of resistin were significantly correlated only with femur BMD in the osteoporosis group, and not significantly correlated with lumbar spine BMD (r = -0.244, P = 0.048 vs r = 0.276, P = 0.56). Leptin did not have a significant correlation with BMD in either the osteoporosis or non-osteoporosis groups (P > 0.05). Adiponectin had a significant negative correlation with BMD of the lumbar spine and femoral neck. The correlation between leptin and resistin are not inconclusive.

Adiponectin is a candidate biomarker of lower extremity bone density in men with chronic spinal cord injury

Adipose tissue is a major regulator of bone metabolism and in the general population obesity is associated with greater bone mineral density (BMD). However, bone-fat interactions are multifactorial, and may involve pathways that influence both bone formation and resorption with competing effects on the skeleton. One such pathway involves adipocyte production of adipokines that regulate bone metabolism. In this study we determined the association between BMD, walking status, and circulating adipokines (adiponectin and leptin) in 149 men with chronic spinal cord injury (SCI). Although adipokine levels did not vary significantly based on walking status, there was a significant inverse association between adiponectin and BMD in wheelchair users independent of body composition. We found no association between adiponectin and BMD in the walkers and no association between leptin and BMD in either group. These findings suggest that for subjects with chronic SCI, walking may mitigate the effect of adiponectin mediated bone loss. For wheelchair users, adipose-derived adiponectin may contribute to SCI-induced osteoporosis because the osteoprotective benefits of obesity appear to require mechanical loading during ambulation.

The relationship between bone mass and body composition in children with hypothalamic and simple obesity

INTRODUCTION

Obesity has been associated with a positive influence on bone mass. This is thought to be due to a mechanical load exerted on the skeleton, together with various hormones and adipocytokines that control appetite and weight, such as leptin, some of which directly affect bone mass. However, there are conflicting reports of the association between fat mass and bone mass in children. Animal studies demonstrate increased bone mass where there is impaired central leptin signalling. Hypothalamic damage can cause abnormal central leptin action, which contributes to the development of obesity.

OBJECTIVE

The objective of this study was to investigate the relationship between body composition and bone mass in hypothalamic and simple childhood obesity, in conjunction with the effect of the adipocytokines, leptin and adiponectin.

DESIGN

This was a cross-sectional study of three groups of children, those with hypothalamic obesity (HO), those with congenital hypopituitarism (CH) and those with simple obesity (SO).

RESULTS

A total of 65 children (HO = 26 [11 males], CH = 17 [eight males] and SO = 22 [15 males]) had body composition assessed using dual-energy X-ray absorptiometry together with measurement of serum leptin and adiponectin. No significant differences were seen in bone mass once bone density (BMD) was adjusted for differences in body size between groups. Significantly elevated levels of leptin and adiponectin were seen in the HO group compared with the SO group (P < 0·01, P < 0·05, respectively).

CONCLUSION

Adiposity is associated with increased bone mass; however, this relationship is complex. Despite the presence of hyperleptinaemia, increased bone mass in the HO group was not seen. This may be due to the effects of other factors such as adiponectin, abnormal hypothalamic signalling, pituitary hormone deficiencies and disruption of normal homoeostatic mechanisms within the hypothalamus.

Haplotype combination of polymorphisms in the ADIPOQ gene promoter is associated with growth traits in Qinchuan cattle

Adiponectin modulates lipid and glucose metabolism in adipose tissues and is also related to bone metabolism. Polymorphisms in the ADIPOQ gene likely have an impact on growth traits in cattle. In this study, we examined the relationship between ADIPOQ polymorphisms and body measurement parameters in Chinese beef cattle. First, we sequenced ADIPOQ and 1.2 kb of DNA upstream of its promoter, and we found 14 polymorphisms. With the luciferase reporter assay, we showed that the two polymorphisms SNP PR_-135 A>G and PR_-68 G>C, which are located in the core region of promoter, influence promoter activity of ADIPOQ. Second, we identified three haplotypes involved in these two polymorphic sites: A (A-135/C-68), B (A-135/G-68), and C (G-135/G-68). Haplotypes B and C are major haplotypes in five Chinese populations of cattle (Qinchuan, Nanyang, Jiaxian, Hazakh, and Chinese Holstein). We studied the effects of these three haplotypes on body measurements, gene expression, and promoter activity, and we found that the genotypes are associated with body measurement parameters in Qinchuan cattle. Individuals with genotype BC (AG/GG) had significantly higher body height and heart girth than others, and this result may be interpreted by the following two observations. The promoter activity with haplotype B (A/G) is significantly higher than those with A (A/C) and C (G/G) in driving reporter gene transcription; the ADIPOQ mRNA level in cattle with genotype BC (AG/GG) is relatively lower than that in cattle with genotype BB (AA/GG).

Osteoblast-specific expression of Fra-2/AP-1 controls adiponectin and osteocalcin expression and affects metabolism

Recent studies have established that the skeleton functions as an endocrine organ affecting metabolism through the osteoblast-derived hormone osteocalcin (Ocn). However, it is not fully understood how many transcription factors expressed in osteoblasts regulate the endocrine function. Here, we show that mice with osteoblast-specific deletion of Fra-2 (Fosl2) have low bone mass but increased body weight. In contrast, transgenic expression of Fra-2 in osteoblasts leads to increased bone mass and decreased body weight accompanied by reduced serum glucose and insulin levels, improved glucose tolerance and insulin sensitivity. In addition, mice lacking Fra-2 have reduced levels of circulating Ocn, but high adiponectin (Adipoq), whereas Fra-2 transgenic mice exhibit high Ocn and low Adipoq levels. Moreover, we found that Adipoq was expressed in osteoblasts and that this expression was transcriptionally repressed by Fra-2. These results demonstrate that Fra-2 expression in osteoblasts represents a novel paradigm for a transcription factor controlling the endocrine function of the skeleton.

Deficiency of adiponectin protects against ovariectomy-induced osteoporosis in mice

Adipokine adiponectin (APN) has been recently reported to play a role in regulating bone mineral density (BMD). To explore the mechanism by which APN affects BMD, we investigated BMD and biomechanical strength properties of the femur and vertebra in sham-operated (Sham) and ovariectomized (OVX) APN knockout (KO) mice as compared to their operated wild-type (WT) littermates. The results show that APN deficiency has no effect on BMD but induces increased ALP activity and osteoclast cell number. While OVX indeed leads to significant bone loss in both femora and vertebras of WT mice with comparable osteogenic activity and a significant increase in osteoclast cell number when compared to that of sham control. However, no differences in BMD, ALP activity and osteoclast cell number were found between Sham and OVX mice deficient for APN. Further studies using bone marrow derived mesenchymal stem cells (MSCs) demonstrate an enhanced osteogenic differentiation and extracellular matrix calcification in APN KO mice. The possible mechanism for APN deletion induced acceleration of osteogenesis could involve increased proliferation of MSCs and higher expression of Runx2 and Osterix genes. These findings indicate that APN deficiency can protect against OVX-induced osteoporosis in mice, suggesting a potential role of APN in regulating the balance of bone formation and bone resorption, especially in the development of post-menopausal osteoporosis.

Relationship between serum omentin-1 level and bone mineral density in girls with anorexia nervosa

BACKGROUND

Adolescents with anorexia nervosa (AN) have low bone mineral density (BMD). Omentin- 1, the main circulating adipocytokine, plays an important role in bone metabolism in healthy individuals. However, their association with bone metabolism in AN is unknown.

METHODS

Serum omentin-1, bone turnover biochemical markers, and BMD were determined in 26 girls with AN and 24 healthy girls (15-18 years old).

RESULTS

Omentin-1 levels increased in AN subjects, and the differences became greater after controlling for fat mass. Omentin-1 was negatively correlated with BMD. In the multiple linear stepwise regression analysis, omentin-1, body mass index and lean mass, but not fat mass, were independent predictors of BMD for the combined group. Significant negative correlations were found between omentin-1 and bone-specific alkaline phosphatase, bone cross-linked N-telopeptides of type I collagen. Omentin-1 was also independently associated with BMD and bone turnover markers in the AN and control groups considered separately.

CONCLUSIONS

Omentin-1 was an independent predictor of BMD in adolescents with AN, and negatively correlated with bone turnover markers. This suggested that omentin-1 may exert a negative effect on bone mass by inhibiting bone formation in girls with AN.

Omentin-1 Stimulates Human Osteoblast Proliferation through PI3K/Akt Signal Pathway

It has been presumed that adipokines deriving from adipose tissue may play important roles in bone metabolism. Omentin-1, a novel adipokine, which is selectively expressed in visceral adipose tissue, has been reported to stimulate proliferation and inhibit differentiation of mouse osteoblast. However, little information refers to the effect of omentin-1 on human osteoblast (hOB) proliferation. The current study examined the potential effects of omentin-1 on proliferation in hOB and the signal pathway involved. Omentin-1 promoted hOB proliferation in a dose-dependent manner as determined by [(3)H]thymidine incorporation. Western blot analysis revealed that omentin-1 induced activation of Akt (phosphatidylinositol-3 kinase downstream effector) and such effect was impeded by transfection of hOB with Akt-siRNA. Furthermore, LY294002 (a selective PI3K inhibitor) and HIMO (a selective Akt inhibitor) abolished the omentin-1-induced hOB proliferation. These findings indicate that omentin-1 induces hOB proliferation via the PI3K/Akt signaling pathway and suggest that osteoblast is a direct target of omentin-1.

Omentin-1, visfatin and adiponectin levels in relation to bone mineral density in Iranian postmenopausal women

The bone and fat interface is implicated in the pathogenesis of postmenopausal osteoporosis. The association between circulating omentin-1 levels and bone mineral density (BMD) in postmenopausal women has never been assessed. A total of 382 healthy postmenopausal women were randomly selected. Omentin-1, visfatin, adiponectin, the receptor activator of nuclear factor-κB ligand (RANKL), osteoprotegerin, high sensitivity C-reactive protein, degradation products of C-terminal telopeptides of type I collagen, and osteocalcin were measured by highly specific enzyme-linked immunosorbent assay methods. BMD was determined for the lumbar spine (L2-L4) and the proximal femur using dual-energy X-ray absorptiometry. In multivariable-adjusted linear regression, serum omentin-1 levels were inversely correlated with BMD at the lumbar spine (β=-0.11, p=0.020). In multiple regression analyses, serum visfatin and adiponectin levels were not significantly correlated with BMD at different skeletal sites after controlling for age, body mass index, and bone-related markers. However, the highest quartile of adiponectin compared to the lowest quartile, after adjusting for potential confounders, revealed an inverse association with BMD in the lumbar spine (β=-0.19, p=0.010). In conclusion, circulating omentin-1 levels had an inverse correlation with BMD at the lumbar spine in Iranian postmenopausal women. To further understand the role of omentin-1 in bone and mineral metabolism, large-scale longitudinal studies focusing on BMD and osteoporotic fractures are warranted.

Effects of 17β-estradiol on adiponectin regulation of the expression of osteoprotegerin and receptor activator of nuclear factor-κB ligand

Adiponectin may exert a negative effect on bone metabolism by regulating osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) expression. However, the action of adiponectin on bone may be influenced by estrogen in women. The present study was undertaken to investigate the effects of 17β-estradiol (E2) on adiponectin-regulated OPG and RANKL expression in human osteoblast. Human osteoblasts were treated with α-MEM containing 10μg/ml adiponectin alone or together with 10(-10) to 10(-8)M E2 for 12-48h. Cells were also treated with α-MEM containing 10μg/ml adiponectin together with 10(-8)M E2 plus p38 agonist-anisomycin or estrogen receptor (ER) antagonist ICI182780 for 48h. The effects of E2 were also investigated by knockdown of ERs or overexpression of p38 MAPK in osteoblasts. Further, we examined the effects of E2 on adiponectin-dependent osteoclastogenesis by the co-culture systems of osteoblast and CD14+ peripheral blood monocytes (PBMCs). Real-time quantitative PCR (RT-PCR) and ELISA were used to detect OPG/RANKL mRNA and their corresponding protein expression, Western Blot was used to analyze the phosphorylated p38 (p-p38) levels. The results showed that E2 blocked adiponectin-induced p38 phosphorylation, decreased adiponectin-regulated OPG/RANKL mRNA and protein expression in a dose- and time-dependent manner. ICI182780 or knockdown of ERs abolished the effects of E2 on adiponectin-dependent p38 phosphorylation and OPG/RANKL expression. Furthermore, anisomycin or overexpression of p38 also reserved the effects of E2 on adiponectin-dependent p38 phosphorylation and OPG/RANKL expression. E2 inhibited adiponectin-dependent osteoclastogenesis in the co-culture systems of osteoblast and CD14+ PBMCs, whereas anisomycin, ICI182780, knockdown of ERs and overexpression of p38 significantly reversed this response. In conclusions, our findings demonstrated, through blocking the activation of adiponectin-induced p38 MAPK, E2 suppressed the adiponectin-regulated OPG/RANKL expression and then inhibited osteoclastogenesis, which suggested that estrogen would suppress the effect of adiponectin on bone metabolism.

Serum adiponectin and bone mineral density in male hemodialysis patients

SUMMARY

Bone mineral density of the 1/3 distal radius, ultra-distal radius, and lumbar spine correlated significantly and negatively with serum adiponectin. There was a significant positive correlation between serum adiponectin and serum NTX. Thus, adiponectin may play a role in mineral and bone disorder in chronic kidney disease stage 5 dialysis (CKD 5D) patients.

INTRODUCTION

Serum adiponectin, an adipocyte-produced hormone, has been reported to correlate negatively with bone mineral density (BMD) in the general population. However, little is known about the association between adiponectin and BMD in patients with CKD.

METHODS

BMD of the 1/3 distal and ultra-distal radius, which are enriched with cortical and cancellous bone, respectively, and the lumbar spine was measured by dual X-ray absorptiometry in 114 Japanese male hemodialysis patients (age 61.0 ± 11.1 years; hemodialysis duration 6.6 ± 3.0 years; 43.9% diabetics). Serum total adiponectin, bone formation marker (bone alkaline phosphatase, BAP), and bone resorption marker (cross-linked N-telopeptide of type I collagen (NTX)) were measured.

RESULTS

The BMD of the 1/3 distal radius, ultra-distal radius, and lumbar spine correlated significantly and negatively with serum adiponectin level (r = -0.229, p = 0.014; r = -0.286, p = 0.002; r = -0.227, p = 0.013, respectively). In multiple linear regression analyses, serum adiponectin was significantly and independently associated with the BMD of the 1/3 distal radius (R(2) = 0.173, p < 0.001) and ultra-distal radius (R(2) = 0.278, p < 0.001) after adjustment of age, hemodialysis duration, body weight, %fat mass, and log [intact PTH], although it was not with the BMD of the lumbar spine. There was a significant positive correlation between serum adiponectin and serum NTX (r = 0.321, p < 0.001), although there was no significant correlation between serum adiponectin and serum BAP.

CONCLUSION

Increased levels of serum adiponectin were associated with decrease in BMD in male hemodialysis patients. Adiponectin may play a role in mineral and bone disorder, possibly in bone resorption, of patients with CKD 5D.

The effects of adiponectin and leptin on changes in bone mineral density

We tested the hypothesis that low leptin and high adiponectin levels are associated with higher rates of bone mineral density (BMD) loss among 3,075 men and women, aged 70-79, from the Health Aging and Body Composition Study. Results suggest that adiponectin, but not leptin, is a risk factor for bone loss in women.

INTRODUCTION

Adiponectin and leptin are hormones secreted by adipose cells that may impact BMD. Few studies have evaluated the longitudinal association of leptin and adiponectin levels with rates of BMD change.

METHODS

Hip and whole-body areal BMD (aBMD) were measured five times using dual-energy X-ray absorptiometry over 10 years (average follow-up time, 7.95 ± 1.92 years). Trabecular lumbar spine volumetric BMD (vBMD) was measured using quantitative computed topography at baseline and year 6 in the Pittsburgh cohort only. Random slope and intercept models were used to account for within person correlation as a result of repeated measures of hip and whole-body aBMD. Linear regression was used to model changes in spine trabecular vBMD.

RESULTS

Among women, the annualized rate of hip aBMD loss in the highest tertile of adiponectin was -0.67% (95% CI -0.77, -0.58) compared to [-0.43% (95% CI -0.51, -0.35)] in the lowest tertile (p trend = 0.019) after adjusting for age, race, BMI, diabetes, baseline hip aBMD, and weight change. In men, hip aBMD loss was greatest in the high adiponectin group (tertile 3), however this association was not significant (p trend = 0.148). After adjusting for weight change in women, the association between higher leptin and lower hip aBMD loss was attenuated and no longer significant (p trend = 0.134). Leptin and adiponectin levels were not associated with whole-body aBMD or trabecular lumbar spine vBMD loss.

CONCLUSIONS

Adiponectin was associated with increased hip aBMD loss in women only, supporting evidence that adiponectin may have an important role in bone health.

Omentin-1 exerts bone-sparing effect in ovariectomized mice

Omentin-1 inhibited osteoblast differentiation in vitro. In co-culture systems of osteoblasts and osteoclast precursors, omentin-1 reduced osteoclast formation by stimulating osteoprotegerin (OPG) and inhibiting receptor activator for nuclear factor κB ligand (RANKL) production in osteoblasts. In vivo, adenovirus-mediated overexpression of omentin-1 suppressed bone turnover and restored bone mineral density (BMD) and bone strength in ovariectomized mice.

INTRODUCTION

Omentin-1 (also intelectin-1) is a recently identified visceral adipose tissue-derived cytokine that is highly abundant in plasma. This study was undertaken to investigate the effects of omentin-1 on bone metabolism.

METHODS

Osteoblast differentiation was assessed by measuring alkaline phosphatase activity, osteocalcin production and matrix mineralization. OPG and RANKL protein expression and secretion in osteoblasts were detected by Western blot and ELISA, respectively. The effect of recombinant omentin-1 on osteoclast formation was examined in co-culture systems of osteoblasts and osteoclast precursors. The effects of intravenous administration of adenoviral-delivered omentin-1 on bone mass, bone strength, and bone turnover were also examined in ovariectomized mice.

RESULTS

In vitro, omentin-1 inhibited osteoblast differentiation, while it had no direct effect on osteoclast differentiation; it also reduced osteoclast formation in the co-culture systems through stimulating OPG and inhibiting RANKL production in osteoblasts. In vivo, adenovirus-mediated overexpression of omentin-1 partially restored BMD and bone strength in ovariectomized mice, accompanied by decreased levels of plasma osteocalcin and tartrate-resistant acid phosphatase-5b and lower serum RANKL/OPG ratios.

CONCLUSION

The present study suggests that omentin-1 ameliorates bone loss induced by estrogen deficiency via downregulating the RANKL/OPG ratio.

Obesity is a risk factor for fracture in children but is protective against fracture in adults: a paradox

With the rise in obesity worldwide, an important debate has developed as to whether excess fat has a detrimental or protective effect on skeletal health in children and adults. Obese children appear to be over represented in fracture groups and recent evidence suggests that fat may be detrimental to bone accrual in children, although this effect may be confined to adolescence during rapid skeletal growth. Fat induced alterations in hormonal factors and cytokines during growth may play a pivotal role in disturbing bone accrual. In contrast, the widely accepted opinion is that fat appears to be protective of bone in adults and minimises bone loss in postmenopausal women. Recent evidence suggests that in adults, site specific fat depots may exert differing effects on bone (with visceral fat acting as a pathogenic fat depot and subcutaneous fat exerting protective effects), and that the effects of fat mass on bone and fracture risk may vary by skeletal site; obesity protects against hip and vertebral fractures but is a risk factor for fractures of the humerus and ankle. The incidence of fracture during adolescence is rising and osteoporosis remains a considerable health burden in older adults. Understanding the effects of fat mass on bone during growth and early adulthood is vital in informing future health strategies and pharmacotherapies to optimise peak bone mass and prevent fracture.

Relationship between serum adiponectin levels and disability-free survival among community-dwelling elderly individuals: The Tsurugaya Project

BACKGROUND

Mortality risk tends to be higher among elderly individuals with higher serum adiponectin levels. The objective of this study was to clarify whether the relationship between adiponectin and a higher risk of disability or death can be explained by physical function, bone mineral density, depression, and malnutrition.

METHODS

We analyzed 505 individuals who underwent comprehensive geriatric assessment and who agreed to provide information on long-term care insurance. The endpoint was the composite outcome of death and incident disability defined as a first certification for any level of care need. Relationships between adiponectin and incident disability or death were estimated using the Cox proportional hazards model.

RESULTS

During 6 years of follow-up, 179 incident disabilities or deaths occurred. Among them, 20 and 23 died with and without disability, respectively. The risk of incident disability or death was significantly higher among participants with adiponectin greater than or equal to 22.4 (90%) than 8.0 or less (25%) mg/L (Hazard ratio: 95% confidence interval, 1.92: 1.01-3.64) in the model adjusted for age, sex, and metabolic risk factors. Adjustment for N-terminal pro-B-type natriuretic peptide and nutritional status did not substantially alter this risk estimate, although the association ceased to be statistically significant. Adjustment for physical function did attenuate the relationship, however, which ceased to be apparent upon exclusion of disability or death occurring within 3 years of follow-up.

CONCLUSION

The relationship between adiponectin and the composite outcome of incident disability and death was at least partly explained by reduced physical function and wasting in participants with higher adiponectin levels.

Preservation of bone mass and biomechanical properties during winter sleep--the raccoon dog (Nyctereutes procyonoides) as a novel model species

It has been established that almost 40% of postmenopausal women in the United States have osteopenia and models to study its prevention are thus urgently needed. Bears (Ursus spp.) displaying winter sleep were previously introduced as promising models to study the treatment of disuse-induced bone loss. The present study examined the potential of another analogous model species, the raccoon dog (Nyctereutes procyonoides), in bone research. Similar to bears, raccoon dogs display prolonged passivity and catabolism in winter, but they are of a moderate body mass, easy to handle and reared on farms. Wild specimens (n=51) were hunted in winter 2007-2008. The bone mineral density of femoral diaphysis and neck was examined with peripheral quantitative computed tomography, after which their mechanical properties were tested with the three-point bending and femoral neck loading tests. A subsample of the specimens was analyzed histologically. While the body mass of the raccoon dogs decreased from 7.0±0.3 to 4.5±0.2 kg (-36%) during winter, the bone mass and biomechanical properties remained unchanged despite of heavy wintertime catabolism similar to bears. Thus, the cortical mineral density remained at approximately 1400 mg/cm(3), the trabecular mineral density at 450 mg/cm(3) and the maximum load of the femoral neck at 700 N. However, in histological samples, the proportion of osteoid perimeter vs. mineralized bone perimeter decreased during wintering. A possible mechanism of bone mass preservation is the endocrine status of overwintering raccoon dogs, which could participate in preventing bone loss.

Adiponectin inhibits osteoclastogenesis and bone resorption via APPL1-mediated suppression of Akt1

Adiponectin is an adipokine playing an important role in regulating energy homeostasis and insulin sensitivity. However, the effect of adiponectin on bone metabolism shows contradictory results according to different research studies. In this study femurs were isolated from genetically double-labeled mBSP9.0Luc/β-ACT-EGFP transgenic mice and were transplanted into adiponectin knock-out mice or wild type mice to investigate the effect of temporary exposure to adiponectin deficiency on bone growth and metabolism. We found that the growth of bone explants in adiponectin knock-out mice was significantly retarded. Histological analysis, microcomputed tomography analysis, and tartrate-resistant acid phosphatase staining revealed reduced trabecular bone volume, decreased cortical bone, and increased osteoclast number in bone explants in adiponectin knock-out mice. We then found that adiponectin inhibits RANKL-induced osteoclastogenesis from RAW264.7 cells and down-regulates RANKL-enhanced expressions of osteoclastogenic regulators including NFAT2, TRAF6, cathepsin K, and tartrate-resistant acid phosphatase. Adiponectin also increases osteoclast apoptosis and decreases survival/proliferation of osteoclast precursor cells. Using siRNA specifically targeting APPL1, the first identified adaptor protein of adiponectin signaling, we found that the inhibitory effect of adiponectin on osteoclasts was induced by APPL1-mediated down-regulation of Akt1 activity. In addition, overexpression of Akt1 successfully reversed adiponectin-induced inhibition in RANKL-stimulated osteoclast differentiation. In conclusion, adiponectin is important in maintaining the balance of energy metabolism, inflammatory responses, and bone formation.

Hyperadiponectinemia enhances bone formation in mice

BACKGROUND

There is growing evidence that adiponectin, a physiologically active polypeptide secreted by adipocytes, controls not only adipose tissue but also bone metabolism. However, a role for adiponectin in bone development remains controversial.

METHODS

We therefore investigated the endocrine effects of adiponectin on bone metabolism using 12-week-old male transgenic (Ad-Tg) mice with significant hyperadiponectinemia overexpressing human full-length adiponectin in the liver.

RESULTS

In Ad-Tg mice, the serum level of osteocalcin was significantly increased, but the levels of RANKL, osteoprotegerin, and TRAP5b were not. Bone mass was significantly greater in Ad-Tg mice with increased bone formation. In contrast, bone resorption parameters including the number of osteoclasts and eroded surface area did not differ between Ad-Tg and their littermates.

CONCLUSIONS

These findings demonstrate that hyperadiponectinemia enhances bone formation in mice.